tltdef(3G)tltdef(3G)NAMEtltdef - defines a texture look-up table
FORTRAN SPECIFICATION
subroutine tltdef(index, nc, len, table, np, props)
integer*4 index, len, nc, np
integer*4 table(*)
real props(np)PARAMETERS
index expects the name of the texture look-up table being defined.
Index 0 is reserved as a null definition, and cannot be
redefined.
nc expects the number of components per table entry.
len expects the length of table in table entries.
table expects a long-word aligned array of packed nc, 8-bit, component
table entries.
np expects the number of symbols and floating point values in props,
including the termination symbol TLNULL. If np is zero, it is
ignored. Operation over network connections is more efficient
when np is correctly specified, however.
props expects the array of floating point symbols and values that
define the texture look-up table. props must contain a sequence
of symbols, each followed by the appropriate number of floating
point values. The last symbol must be TLNULL.
DESCRIPTION
Texture coordinates, s,t,r may be specified at geometry vertices,
similarly to color, depth, and vertex normals. The texture coordinates
are interpolated from the values specified at the vertices for each
screen pixel touched by the geometry. A texture function maps the
texture coordinates s,t, or s,t,r, corresponding to a screen pixel into
nc values, called texture function outputs, using an image and a set of
properties. The texture function outputs may be translated with a texture
look-up table. The texture lookup outputs are used by the texture
environment function to modify the screen pixel color.
The texture look-up table is defined by tlutdef and selected by tlutbind.
texdef2d and texdef3d define a texture function and texbind selects which
texture function definition to use. The texture environment function is
defined by tevdef and selected by tevbind. The texture coordinates are
specified with the t family of commands.
The texture look-up table allows the texture function outputs to be
translated via the texture look-up table. The interaction between texture
look up tables and textures with differing number of components is as
follows:
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tltdef(3G)tltdef(3G)
tlut nc texture nc action
------------------------------
2 1 I looks up I,A
2 I,A looks up I,A
3 R,G,B passes through unchanged
4 R,G,B,A passes through unchanged
3 1 I looks up R,G,B
2 I,A passes through unchanged
3 R,G,B looks up R,G,B
4 R,G,B,A passes through unchanged
4 1 I looks up R,G,B,A
2 I looks up R,G,B; A looks up A.
3 R,G,B,B looks up R,G,B,A
4 R,G,B,A looks up R,G,B,A
If the tlutdef parameter nc is not equal to the texdef parameter nc,
tlutdef's nc determines which texture environment equation is used. For
example, if tlutdef's nc is 2 and a 1-component texture is used, texture
environment TVMODU will scale red, green, and blue by lookup output I and
alpha by lookup output A.
There are no properties currently defined for this command. Different
sized components may be supported in the future.
SEE ALSO
afunct, scrsub, t, tevbin, tevdef, texbin, texdef, texgen
NOTES
IRIS-4D G, GT, GTX, VGX, VGXT models, and the Personal Iris, Iris Indy,
and Iris Indigo, do not support texture look up tables. tlutdef is
ignored by these machines. Use getgde to determine whether texture
mapping is supported.
BUGStltdef is not supported on Impact.
On Infinite Reality one and three component texture images on Infinite
reality always return the 255th entry in the alpha table for two and four
component tluts.
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